Rackets have been used ubiquitously for many years in sports including tennis, squash, and badminton, among others. Rackets generally include a handle for the user to grip with their hand, a shaft (also referred to as the ‘neck’ of the racket) connecting the handle to a hoop-shaped frame or rim (also referred to as the ‘head’ of the racket), and a stringbed formed from one or more strings drawn through and suspended between holes in the rim.
When used in practice—in tennis, for example—a player swings the racket in an attempt to strike an approaching ball in a manner that redirects the ball along a desired trajectory to a desired location. Many factors affect the user's ability to precisely redirect the ball along the desired trajectory using the racket. Some of these factors include: (i) the stringbed stiffness profile (ii) the tensile strength and gauge of the string material, (iii) the string pattern, (iv) the location and angle with which the ball makes contact with the stringbed, (v) the mechanical strength of the racket components (e.g. rim, handle, etc.), (vi) the size of the racket head, (vii) the structural features of the holes within the rim (or of the grommets disposed in the holes when grommets are used), and (viii) the compressive strength of the ball, among many other factors. The control of some of these factors is largely dependent on the skill level of the player, e.g., factor (iv) above. However, control of certain other factors can largely depend on the equipment and methods used to manufacture, produce and assemble the racket itself. Indeed, many devices have been developed to improve control of one or more of factors (i), (ii), (v), (vi), and (vii) above, with the goal of enhancing the overall performance and consistency of the racket. However, currently available devices still fail to provide an adequate system and/or method for precisely and accurately tensioning the strings of a racket. In particular, currently available devices used for tensioning the strings of a racket cannot effectively create a uniform and/or symmetric stringbed stiffness from one side of the racket to the other (i.e. from left to right and/or top to bottom of the stringbed).
Stringbed stiffness is a measure of the extent to which the strings of a racket deflect upon impact. The stiffness of the stringbed is directly related to a player's ability to control the trajectory and placement of a ball (e.g. a tennis ball). In particular, decreasing the stringbed stiffness can increase the amount of time that the ball actually stays in contact with the strings (“dwell time”) through the arc of the player's swing, thereby allowing more energy to return to the ball on rebound. Dwell time relates to ball pocketing, and may contribute to a player's ability to produce spin on the ball. Players can often achieve more control over their shots if they are able to control the amount of spin on the ball when returning the ball to their opponent, e.g., adding top-spin to the ball can cause the ball to drop short (i.e. drop in) earlier, even when hit with additional power. Alternatively, increasing the stringbed stiffness can do just the opposite, i.e., reduce the dwell time and transfer much more of the energy to the strings and racket instead of back to the ball on rebound. Accordingly, depending on the preference of the player, increasing or decreasing the stringbed stiffness can provide significant benefits and/or drawbacks to the player's performance during a game.
For example, as described above, decreasing the stringbed stiffness allows the strings to return more energy to the ball on rebound, thereby increasing the rebound velocity of the ball. So by decreasing the stiffness of the stringbed, a player may return the ball to her opponent with more power than he or she might otherwise be able. However, because dwell time increases as stringbed stiffness decreases, some players experience added difficulty in controlling the direction and/or trajectory of the ball. In particular, because the ball remains in contact with the stringbed for a longer period of time during the arc of the player's swing (i.e. along a greater portion of the swing path), the change in the racket's position and orientation from the time the ball first contacts the stringbed to the time when the ball finally rebounds off of the stringbed increases. The timing difference can be difficult for a player to resolve in real-time, and can thus introduce additional error and inconsistency into the player's game (i.e. their performance). Even trained players find it difficult to master the various timing factors at play in a game (e.g. the consistency and speed of their swing, the timing and rotation of their body movements during a swing, the speed and angle of an approaching ball, etc.), so the added timing variability introduced by a decreased stringbed stiffness can accentuate the other timing errors the player might already be struggling to perfect. In sum, while a looser configuration can enable a player to harness more power when hitting the ball, the increase in power often comes at the expense of a decrease in control.
On the other hand, increasing the stringbed stiffness decreases dwell time and causes the stringbed to deflect less on impact with the ball. Because the ball is in contact with the stringbed for a shorter period of time over the path/arc of the player's swing, the player may more easily control the direction and/or trajectory of the ball. In particular, when the stringbed stiffness is sufficiently stiff, the time period the ball is in contact with the racket stringbed during a given hit is so short that some player's subconsciously hit the ball as though it instantaneously rebounds off the racket upon contact. Though rebound is not in fact instantaneous, the error in timing offset is nevertheless minimized as the time period the ball is in contact with the racket stringbed approaches zero (approaches an instantaneous rebound). Accordingly, because the player can better approximate the position and orientation of the racket through the arc of their swing when the ball rebounds from a stiffer stringbed, players often experience an enhanced level of control over the ball when they use stiffer stringbeds. However, as indicated above, the price paid for increased control is often a loss of power. That is, increasing the stringbed stiffness causes the racket and strings to absorb much more of the energy of impact rather than returning that energy to the ball. In sum, a tighter/stiffer stringbed configuration enables players to maintain more control when hitting the ball, but that control comes at the expense of a decrease in overall power when returning the ball to an opponent.
Because of the advantages and drawbacks of increasing or decreasing the stringbed stiffness of a racket, professional players generally develop very specific preferences with regard to stringbed stiffness. Some players are able to fine tune their ability to resolve the timing offset experienced with a looser stringbed, and therefore prefer the looser configuration to give the ball more power/velocity when returning it to an opponent. Other players are willing to give up the increased power provided by a looser stringbed in order to maintain adequate control over the ball and enhance their ability to accurately place the ball in a given location on the court. For many players, the optimal stiffness configuration will balance the benefits and drawbacks identified above to best complement the user's skill level and physical capabilities. In any case, once a player identifies the stringbed stiffness most suitable for their skillset, most players will go to great lengths to have their rackets strung to display that optimal level of stiffness. Moreover, because the stiffness from one point on the stringbed to another may differ (the collection of stiffness measures across the entire stringbed being referred to herein as the stringbed stiffness profile), players may also go to great lengths to have their rackets strung with the greatest degree of uniformity and/or symmetry as possible. Indeed, a non-uniform or asymmetric stringbed stiffness profile may cause just as much frustration for a player as having an overall (e.g. average) stringbed stiffness that is too loose or too tight.
As indicated previously, the stiffness of the stringbed at any given location on the stringbed is directly related to the combined stiffness and tension measures of the individual string segments affecting that portion of the stringbed. Because the string segments are woven together to form the stringbed, the tension in each string segment has at least some effect on the stiffness displayed at any given point on the stringbed. Thus, in order to achieve the desired stringbed stiffness profile/configuration having the uniformity and symmetry the player expects (e.g. symmetry of the stiffness gradient from the center to the edges of the racket, for example) great care is required in tensioning each length or segment of string when a racket is strung. Even slight variations or imperfections in the stringing and tensioning process can be accentuated over time and have a substantial impact on the symmetry of the stringbed stiffness profile.
When discussing the symmetry and/or uniformity of a racket's stringbed stiffness profile, it should be noted that the string segments of a racket will often be considered in pairs (e.g. a pair of complementary string segments). In particular, because a racket head is symmetric about its longitudinal axis, each string segment on the racket will generally have a complementary segment that is of the same length, runs in the same direction, and is located at an equal distance (albeit in the opposite direction) from the center-line of the racket head. Each such set of string segments is called a pair for purposes of this disclosure. To achieve a stringbed stiffness profile that is symmetric, each segment within a pair should ideally display an equal tension. However, as explained below, conventional tensioning systems have certain limitations that make it difficult to achieve such symmetry.
First, when the tensioning process is carried out with conventional devices, string segments are tensioned one-at-a-time. Accordingly, a significant amount of time elapses between tensioning a given string segment and tensioning its complement (i.e. the other string segment of the pair). Unfortunately, the string material (e.g. nylon, natural gut, etc.) itself begins to creep (i.e. slacken) almost immediately upon being tensioned. So by the time the racket tensioner begins tensioning the second segment of the pair, the first segment will have already lost some amount of tension. What's more, the rate of creep in a tensioned string changes with time, so consequently the tension disparity between two string segments can be further exacerbated as time progresses.
What makes the above issue even more complicated—especially for those skilled racket tensioners who have recognized this dilemma—is the fact that different string materials behave in different ways. That is, the various stringing materials commonly used (e.g. natural gut, synthetic gut, polyester, Kevlar, Vectran, Zyex, polyolefin, etc.) differ in their mechanical properties, and they behave differently under tension. For example, polyester strings tend to experience creep (i.e. deform permanently under the influence of a mechanical stress) at a higher rate than natural gut. This irregularity further complicates the string tensioning process for most tensioners, and can further accentuate the stringbed symmetry problems discussed above. Indeed, when conventional devices are used, string segments of a pair may vary in tension by as much as 10 pounds-force (44.48 Newtons) or more.
Second, conventional stringing devices utilize either floating dual-string clamps or stationary single-string clamps to secure string segments in place post-tensioning. Floating clamps are configured with two or more clamping mechanisms configured to hold one string in place by clamping it to an already tensioned neighboring string. That is, a floating clamp uses the structure of a neighboring string to retain the tension in a subsequently tensioned string. As their name indicates, floating clamps float or hang separate from the rest of the stringing device (unlike stationary clamps), being supported only by the string(s) they are clamped onto. One well-known problem that arises when using floating clamps is that the clamp itself rotates slightly when a second segment (the segment secured in place via clamping to the first segment) is released from the tensioning mechanism (e.g. the drop-weight, crank, etc.). In particular, because the first string segment isn't completely rigid (even once it is tensioned), it will bend slightly when it becomes subject to the forces brought on by the release of the second string segment from the tensioning mechanism (thereby rotating and/or shifting the position of the floating clamp relative to its original position). This rotation and/or shift of the floating clamp introduces additional slack and variation into both string segments. The first segment slackens because the additional force applied by the second segment accelerates the amount and rate of creep in the first segment, and the second segment slackens because the bending of the first segment translates into longitudinal relaxation of the second segment. This additional slackening gives rise to further asymmetries throughout the stringbed when using floating clamps.
Because of the problems that arise when using floating clamps, many conventional racket tensioning systems have instead employed one or more stationary single-string clamps. Stationary single-string clamps are clamps that hold just a single string at a time, but which are adjustably secured to the structure of the stringing device itself (usually the turntable) to more securely hold the string segment in place. Thus, instead of using a neighboring string segment to secure the position of a subsequently tensioned string segment (as with floating clamps), the stationary clamps use the structure of the stringing device itself to secure each string segment. Because stationary clamps provide a stronger and more rigid structure to secure the position of a tensioned string segment, the tension in the string segment is retained more effectively. However, even with the added strength provided by these stationary single-string clamps, there is still a little play (i.e. movement) observed in these conventional clamps when string segment held by these clamps are released from the tensioning mechanism. And because these clamps only hold a single string at a time (and further that slight movement in the clamp is not translated equivalently to string pairs), even conventional single-string clamps can give rise to tension inconsistencies throughout the stringbed.
Third, and with respect to conventional drop-weight tensioners in particular, the weighted component utilized in such devices cannot be adjusted with precision. More specifically, the weighted component in such devices is configured be manually moved up and down a rod and be secured in a desired position using a fastening mechanism. Of course, the position of the weighted component along the length of the rod corresponds to the amount of force that will ultimately be applied to a given string segment when the weighted component is dropped (i.e. released or allowed to fall). In conventional models, however, to move the weighted component up or down the rod the user must loosen the fastener, slide the weighted component into the desired position by hand alone, and then tighten the fastener to lock the weighted component into place. Because the weighted component moves freely along the length of the rod when unfastened, the precision with which the component is moved to the right location on the rod is only as exact as the user's ability to position it. Indeed, because of this, a user's ability to fine-tune the force applied to the string segment by making very small changes in the position of the weighted component along the rod is quite limited. As such, the imprecision of such a system gives rise to further inconsistencies and asymmetries throughout the stringbed.
These issues, as discussed, give rise to asymmetry and imprecision in the tension of individual string segments and overall stiffness profile displayed stringbed. Accordingly, there is a long-felt need for systems, methods and devices that can provide more precision and symmetry in tensioning the strings of a racket.